Bifurcated oil scavenge system for a gas turbine engine

ABSTRACT

An oil scavenge system includes a tangential scavenge scoop and a settling area adjacent thereto which separately communicate with a duct which feeds oil into an oil flow path and back to an oil sump. A shield is mounted over the settling area to at least partially shield the collecting liquid oil from interfacial shear. A multiple of apertures are located through the shield to permit oil flow through the shield and into the duct. The scavenge scoop forms a partition which separates the duct into a first portion and a second portion. The first portion processes upstream air/oil mixture that is captured by the tangential scoop while the second portion receives the oil collected in the settling area.

BACKGROUND OF THE INVENTION

The present invention relates to oil systems for gas turbine engines,and more particularly to an oil scavenge system.

Gas turbine engines employ high-speed bearings that require a continuoussupply of oil for lubrication and cooling. For optimum performance, theoil flow must be properly directed into and away from the bearings.Failing to remove or scavenge oil from the bearing may be as detrimentalto the bearing as insufficient oil flow because the churning ofunscavenged oil within the bearing can rapidly lead to overheating.

In a conventional lubrication system, oil is supplied to the rollingelements of the bearings under pressure and then relies on gravity orits dynamics to drain back to a reservoir.

One effective way to accomplish the return flow is to maintain an open,straight, and unrestricted passageway from the bearing back to the sump.This often requires that the air/oil mixture be redirected from acircumferential path within the bearing to an exit pipe, which isarranged axially or radially thereto.

To redirect the swirling bearing compartment two-phase air/oil mixturefrom the circumferential path direction to the axial or radial exit pipeflow direction, current oil scavenge systems use tangential scoops thattransition into an integrated 90 deg bend that connects to the exitpipe. Due to minimum length requirements for the 90 deg bend,conventional scavenge ports may have an inlet plane located severaldegrees upstream of bottom dead center (BDC). Oil provided to thebearing compartment cavity downstream of the inlet plane needs to becarried by interfacial shear forces around the compartment to reach theinlet plane. Otherwise the oil may begin to collect in the cavity. Theformer typically occurs at high power settings while the lattertypically occurs at low power settings such as motoring, windmilling, oridle. To permit drainage of collected oil that has not been captured bythe tangential scoop, a drain is typically integrated into thetangential scoop/bend arrangement at BDC.

Although effective for particular compartment sump dimensions andmoderate rotational speeds, as engine core size constraints become moreaggressive and speeds increase, disadvantages of conventional scavengeport arrangements may begin to occur. In particular, as the size of thesump region decreases, the distance between the compartment seals andthe free surface of the collected oil pool decreases. The reducedseparation may increase the potential for oil leakage. Furthermore,interfacial shear acting on the gas/liquid interface may drive oil awayfrom the drain at BDC. The oil may then form a recirculation zonedownstream at BDC. Oil recirculation zones tend to contaminate seals,which may ultimately result in oil leakage from the compartment.

Accordingly, it is desirable to provide an oil scavenge system whichefficiently directs a two-phase air/oil mixture with highcircumferential flow velocity and significant velocity differencesbetween both media into an axial or radial flow direction within compacthigh speed bearing compartments without oil leakage and at all operatingconditions.

SUMMARY OF THE INVENTION

The oil scavenge system according to the present invention provides atangential scavenge scoop and a settling area adjacent thereto whichseparately communicate with a duct which feeds oil into an oil flow pathand back to an oil sump. The settling area is downstream of the scavengescoop relative to a rotational direction defined about the axis ofrotation of the engine.

A shield is mounted over the settling area to shield the collectingliquid oil from interfacial shear. A multiple of apertures are locatedthrough the shield to permit oil flow through the shield and into theduct.

The scavenge scoop forms a partition which separates the duct into afirst portion and a second portion. The duct is located at bottom deadcenter of the housing and the partition generally bisects the duct butmay alternatively be biased in a particular direction. The first portionis sufficient to process the upstream air/oil mixture that is capturedby the tangential scoop while the second portion receives the oilcollected in the settling area.

The present invention therefore provides an oil scavenge system whichefficiently directs a two-phase air/oil mixture with highcircumferential flow velocity and significant velocity differencesbetween both media into an axial or radial flow direction within compacthigh speed bearing compartments without oil leakage and at all operatingconditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a general schematic sectional view of an exemplary gas turbineengine embodiment for use with the present invention;

FIG. 2 is a general schematic sectional view of a mid bearingcompartment illustrated in FIG. 1;

FIG. 3 is a rear expanded perspective view of a housing portion with anoil scavenge system of the present invention;

FIG. 4 is a rear expanded perspective view of the housing portionwithout a shield component illustrated in FIG. 3; and

FIG. 5 is a front expanded perspective view of a housing portion with anoil scavenge system of the present invention;

FIG. 6 is a sectional view of an oil duct from the oil scavenges systemtaken along line 6—6 in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a general schematic sectional view of a gas turbineengine 10. The gas turbine engine 10 is defined about an enginecenterline A about which the various engine sections rotate. Generally,the engine 10 includes a fan section 12, a low pressure compressorsection 14, a high pressure compressor section 16, a combustor section18, a high pressure turbine section 20 and a low pressure turbinesection 22. It should be understood that although a particulararrangement is disclosed in the illustrated embodiment, otherarrangements will benefit from the instant invention.

The sections are mounted about a main shaft 24 supported by various highspeed bearings. One bearing 27 is located within a mid bearingcompartment 28. The bearing 27 and compartment 28 receives lubricationand cooling from oil which is provided through jets and is thencollected through an oil scavenge system which returns the oil to an oilsump through a flow path 29 (FIG. 2). It should be understood thatvarious bearing systems will benefit from the present invention.

Referring to FIG. 2, the mid bearing compartment 28 seals 30, 32 preventoil leakage from a compartment front 34 and a compartment rear 36. Airand oil flows mix inside the bearing compartment 28 and generate a flowpattern about the engine axis of rotation A. The oil flow patterngenerally operates as follows: Oil particles coalesce along the internalbearing compartment partitions and form a liquid partition film whichcontains air bubbles. In the radial space between the rotating mainshaft 24 and the liquid oil film, a mixture of air and dispersed oilparticles swirl in a circumferential direction at a velocity greaterthan the liquid oil film flow along the compartment partitions. As aresult, the oil film flow is exposed to high shear stresses at theair/oil film interface. Film thickness and velocity distributions insidethe bearing compartment 28 are driven by the magnitude of thatinterfacial shear and superimposed effects of gravitational forces.

To achieve compartment functionality, i.e. low temperatures and low heatgeneration without risk of oil leakage, air and oil flows are dischargedto an oil scavenge system 38 which communicates with the oil sumpthrough the flow path 29. It should be understood that variousconventional oil injection jets and breather systems may be utilizedwith the present invention.

Referring to FIG. 3, the oil scavenge system 38 is formed within ahousing 40 which forms a portion of the mid bearing compartment 28 (FIG.2). It should be understood that although a cylindrical housing isdisclosed in the illustrated embodiment, various housing configurationswhich utilize oil scavenge system will benefit from the presentinvention.

The oil scavenge system 38 generally includes a scavenge scoop 42 and asettling area 44 adjacent thereto. The scavenge scoop 42 defines ascavenger scoop intake 45 directed in a circumferential directionrelative a rotational direction defined about said axis of rotation tocollect air and oil flows which swirl in a circumferential directionabout said axis of rotation. The scavenge scoop 42 and the settling area44 separately communicate with a duct 46 (also illustrated in FIG. 4)which feeds oil into the flow path 29. Preferably, the settling area 44is downstream of the scavenge scoop 42 relative a rotational direction Rdefined about the axis or rotation A. That is, the settling area 44 isopposite the scavenge scoop 42 (FIG. 4) to collect oil that is in moreof a liquid form. Various baffles 43 or the like may additionally extendfrom the scoop 42 to assist in direction of the oil mixture.

Preferably, a shield 48 is mounted over the settling area 44 to at leastpartially shield the collecting liquid oil from interfacial shear. Amultiple of apertures 50 are located through the shield 48 to permit oilflow through the shield 48 and into the duct 46. It should be understoodthat the shield 48 alternatively be cast directly into the housing.

Referring to FIG. 5, the scavenge scoop 42 forms a partition 51 whichseparates the duct 46 into a first portion 52 and a second portion 54(also illustrated FIG. 6). Preferably a downstream wall 47 of thescavenger scoop 42 forms the partition 51 (also illustrated in FIG. 4)Preferably, the duct 46 is located at bottom dead center (BDC) of thehousing 40 and the partition 51 generally bisects the duct 46. Thepartition 51 may alternatively be biased in a particular direction so inresponse to flow conditions of the expected two-phase air/oil mixture toprovide efficient operation with low residence time and withoutrecirculation zones and hot spots.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the normal operational attitude of the vehicle andshould not be considered otherwise limiting.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent invention.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The preferredembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. An oil scavenge system for a gas turbine engine comprising: a housing defined about an axis of rotation, said housing defining a duct; a scavenge scoop within said housing which includes an intake generally directed in a circumferential direction relative a rotational direction defined about said axis of rotation, said scavenge scoop in communication with a first portion of said duct, said scavenge scoop defining a partition which separates said duct into said first portion and a second portion; and a settling area within said housing adjacent said scavenge scoop, said settling area in communication with said second portion of said duct opposite said partition.
 2. The oil scavenge system as recited in claim 1, wherein said housing is located within a mid bearing compartment of a gas turbine engine.
 3. The oil scavenge system as recited in claim 1, wherein said settling area is downstream of said scavenge scoop relative to said rotational direction defined about said axis or rotation.
 4. The oil scavenge system as recited in claim 1, wherein said duct is generally parallel to said axis of rotation.
 5. The oil scavenge system as recited in claim 1, wherein said duct is located at bottom dead center of said housing.
 6. The oil scavenge system as recited in claim 1, wherein said axis of rotation comprises a centerline of said gas turbine engine.
 7. The oil scavenge system as recited in claim 1, further comprising a shield at least partially covering said settling area.
 8. The oil scavenge system as recited in claim 1, wherein said housing is a gas turbine engine housing portion.
 9. The oil scavenge system as recited in claim 1, wherein said settling area is downstream of said scavenge scoop relative to said rotational direction defined about said axis or rotation.
 10. An oil scavenge system for a gas turbine engine comprising: a housing defined about an axis of rotation within which an air-oil mixture flow swirls in a circumferential direction about said axis of rotation; a scavenge scoop within said housing which includes an intake generally directed in opposition to the circumferential direction, said scavenge scoop defining a downstream scavenger scoop wall relative said circumferential direction which forms a partition between a first duct portion and a second duct portion, said scavenge scoop in communication with said first duct portion; and a settling area within said duct downstream of said scavenge scoop, said settling area in communication with said second duct portion.
 11. The oil scavenge system as recited in claim 10, wherein said partition bisects a duct defined between said first duct portion and said second duct portion.
 12. The oil scavenge system as recited in claim 10, wherein said housing is generally cylindrical, sad scavenge scoop located within an inner wall of said housing.
 13. The oil scavenge system as recited in claim 10, wherein said housing is generally cylindrical, sad scavenge scoop located within an inner wall of said housing.
 14. The oil scavenge system as recited in claim 10, further comprising a baffle which extends from said scavenge scoop generally transverse to said circumferential direction.
 15. The oil scavenge system as recited in claim 14, wherein said baffle extends from said downstream scavenger scoop wall.
 16. The oil scavenge system as recited in claim 10, wherein said duct is located at bottom dead center of said housing.
 17. The oil scavenge system as recited in claim 10, wherein said housing is located within a mid bearing compartment of a gas turbine engine, said axis of rotation comprises a centerline of said gas turbine engine.
 18. The oil scavenge system as recited in claim 10, further comprising a shield at least partially covering said settling area.
 19. The oil scavenge system as recited in claim 18, further comprising a multiple of apertures located through said shield.
 20. The oil scavenge system as recited in claim 10, wherein said duct is located at bottom dead center of said housing generally parallel to said axis of rotation. 